Expression vectors for an improved protein secretion

ABSTRACT

The aim of the invention is to improve the secretion of a protein from a host cell in order to increase the product yield of protein in a fermentation process. This is achieved by an expression vector comprising a promoter sequence and a nucleic acid sequence that codes for a protein. The protein comprises a signal peptide and an additional amino acid sequence, and the signal peptide comprises an amino acid sequence that is at least 80% identical to the amino acid sequence specified SEQ ID NO: 2, at least 80% identical to the amino acid sequence specified in SEQ ID NO: 4, at least 80% identical to the amino acid sequence specified in SEQ ID NO: 6, or the signal peptide comprises an amino acid sequence that is structurally homologous to at least one of said sequences.

This application is a National Stage application of InternationalApplication No. PCT/EP2012/059901, filed May 25, 2012. This applicationalso claims priority under 35 U.S.C. §119 to German Patent ApplicationNo. 10 2011 118 032.3, filed May 31, 2011.

The invention is in the field of biotechnology, more particularlymicrobial protein synthesis. The invention relates in particular toexpression vectors for preparing proteins and proposes, in addition,host cells comprising such expression vectors. The invention furtherrelates to methods and uses of such expression vectors and host cellsfor protein preparation.

For the preparation of proteins, use can be made of host cells, moreparticularly microorganisms, expressing the genes of the proteins ofinterest. The gene of a protein of interest (transgene) is generallyintroduced into the host cells in such a way that it is expressedthereby. Frequently, it is present on a so-called expression vectortogether with one or more promoter sequences (promoters), which permitgene expression.

For industrial-scale, biotechnological production, the host cells inquestion are cultured in fermenters which are adapted accordingly to themetabolic properties of the cells. During the culture, the host cellsmetabolize the supplied substrate and form the desired product, which,after the end of the fermentation, is usually separated from theproduction organisms and is purified and/or concentrated from thefermenter slurry and/or the fermentation medium.

It is inherently desirable to obtain a very high product yield in thefermentation. The product yield is dependent on multiple factors, forexample the host cells usually form, in addition to the product actuallydesired, a multiplicity of further substances which are generally of nointerest. In addition, the expression of a transgene and thus theproduct yield depends substantially on the expression system used. Forexample, the international patent application WO 91/02792 discloses theimproved fermentative production of an alkaline protease from Bacilluslentus in an optimized Bacillus licheniformis strain under the controlof gene regulatory sequences from Bacillus licheniformis, moreparticularly the Bacillus licheniformis promoter.

For the industrial production of proteins, for example hydrolyticenzymes, preference is given to using host cells capable of secretinglarge amounts of the protein into the culture supernatant, makingelaborate cell disruption, which is necessary in intracellularproduction, redundant. For this purpose, preference is given to usinghost cells, for example Bacillus species, which can be cultured usingcost-effective culture media in efficient high-cell-density fermentationprocedures and are capable of secreting multiple grams per liter of thetarget protein into the culture supernatant. Usually, the protein to besecreted is expressed by expression vectors which have been introducedinto the host cell and encode the protein to be secreted. The expressedprotein usually comprises a signal peptide (signal sequence) whichbrings about the export thereof from the host cell. The signal peptideis usually part of the polypeptide chain translated in the host cell,but it can be additionally cleaved posttranslationally from the proteininside or outside the host cell.

Especially for this extracellular production of heterologous proteins,there are, however, numerous bottlenecks and a corresponding high demandfor optimization of the secretion processes. One of these bottlenecks isthe selection of a signal peptide which allows efficient export of thetarget protein from the host cell. Signal peptides can, in principle, benewly combined with proteins, more particularly enzymes. For example,the publication by Brockmeier et al. (J. Mol. Biol. 362, pages 393-402(2006)) describes the strategy of screening a signal peptide libraryusing the example of a cutinase. However, not every signal peptide alsobrings about adequate export of the protein under fermentationconditions, more particularly industrial or industrial-scalefermentation conditions.

It is therefore an object of the invention to improve the secretion of aprotein from a host cell and, as a result, to increase the proteinproduct yield in a fermentation procedure.

The invention provides an expression vector comprising

a) a promoter sequence and

b) a nucleic acid sequence which encodes a protein, the proteincomprising a signal peptide and a further amino acid sequence and thesignal peptide comprising an amino acid sequence which is at least 80%identical to the amino acid sequence specified in SEQ ID NO: 2 or is atleast 80% identical to the amino acid sequence specified in SEQ ID NO: 4or is at least 80% identical to the amino acid sequence specified in SEQID NO: 6, or the signal peptide comprising an amino acid sequence whichis structurally homologous to at least one of these sequences.

It was found that, surprisingly, an expression vector encoding a proteinhaving such a signal peptide achieves improved secretion of the proteinfrom a host cell containing the expression vector and expressing thenucleic acid sequence b). As a result, it is possible in preferredembodiments of the invention to increase the protein product yield in afermentation procedure.

An expression vector is a nucleic acid sequence which enables theprotein to be expressed in a host cell, more particularly amicroorganism. It comprises the genetic information, i.e., that nucleicacid sequence (gene) b) which encodes the protein.

The expression of a nucleic acid sequence is its rendering into the geneproduct(s) encoded by said sequence, i.e., into a polypeptide (protein)or into multiple polypeptides (proteins). The terms polypeptide andprotein are used synonymously in the present application. For thepurposes of the present invention, expression consequently means thebiosynthesis of ribonucleic acid (RNA) and proteins from the geneticinformation. Generally, the expression comprises the transcription,i.e., the synthesis of a messenger ribonucleic acid (mRNA) on the basisof the DNA (deoxyribonucleic acid) sequence of the gene, and thetranslation of the mRNA into the corresponding polypeptide chain, whichmay additionally be modified posttranslationally. The expression of aprotein consequently describes the biosynthesis thereof from the geneticinformation which is provided according to the invention on theexpression vector.

Vectors are genetic elements consisting of nucleic acids, preferablydeoxyribonucleic acid (DNA), and are known to a person skilled in theart in the field of biotechnology. Particularly when used in bacteria,they are specific plasmids, i.e., circular genetic elements. The vectorscan, for example, include those which are derived from bacterialplasmids, from viruses or from bacteriophages, or predominantlysynthetic vectors or plasmids containing elements of very diverseorigin. With the further genetic elements present in each case, vectorsare capable of establishing themselves in host cells, into which theyhave been introduced preferably by transformation, over multiplegenerations as stable units. In this respect, it is insignificant forthe purposes of the invention whether they are establishedextrachromosomally as separate units or are integrated into a chromosomeor chromosomal DNA. Which of the numerous systems is chosen depends onthe individual case. Critical factors may, for example, be theachievable copy number, the selection systems available, includingespecially the antibiotic resistances, or the culturability of the hostcells capable of vector uptake.

Expression vectors may, furthermore, be regulatable through changes inthe culture conditions, for example the cell density or the addition ofparticular compounds. An example of such a compound is the galactosederivative isopropyl-β-D-thiogalactopyranoside (IPTG), which is used asan activator of the bacterial lactose operon (lac operon).

An expression vector further comprises at least one nucleic acidsequence, preferably DNA, having a control function for the expressionof the nucleic acid sequence b) encoding the protein (a so-called generegulatory sequence). A gene regulatory sequence is, in this case, anynucleic acid sequence which, through its presence in the particular hostcell, affects, preferably increases, the transcription rate of thenucleic acid sequence b) which encodes the protein. Preferably, it is apromoter sequence, since such a sequence is essential for the expressionof the nucleic acid sequence b). However, an expression vector accordingto the invention can also comprise yet further gene regulatorysequences, for example one or more enhancer sequences. An expressionvector for the purposes of the invention consequently comprises at leastone functional unit composed of the nucleic acid sequence b) and apromoter (expression cassette). It can, but need not necessarily, bepresent as a physical entity. The promoter brings about the expressionof the nucleic acid sequence b) in the host cell. For the purposes ofthe present invention, an expression vector can also be restricted tothe pure expression cassette composed of promoter and nucleic acidsequence b) to be expressed, it being possible for said expressioncassette to be integrated extrachromosomally or else chromosomally. Suchembodiments of expression vectors according to the invention eachconstitute a separate embodiment of the invention.

The presence of at least one promoter is consequently essential for anexpression vector according to the invention. A promoter is thereforeunderstood to mean a DNA sequence which allows the regulated expressionof a gene. A promoter sequence is naturally a component of a gene and isoften situated at the 5′ end thereof and thus before the RNA-codingregion. Preferably, the promoter sequence in an expression vectoraccording to the invention is situated 5′ upstream of the nucleic acidsequence b) encoding the protein. The most important property of apromoter is the specific interaction with at least one DNA-bindingprotein or polypeptide which mediates the start of the transcription ofthe gene by means of an RNA polymerase and is referred to as atranscription factor. Multiple transcription factors and/or furtherproteins are frequently involved at the start of the transcription bymeans of an RNA polymerase. A promoter is therefore preferably a DNAsequence having promoter activity, i.e., a DNA sequence to which atleast one transcription factor binds at least transiently in order toinitiate the transcription of a gene. The strength of a promoter ismeasurable via the transcription rate of the expressed gene, i.e., viathe number of RNA molecules, more particularly mRNA molecules, generatedper unit time.

Preferably, the promoter sequence (a) and the nucleic acid sequence (b)are behind one another on the expression vector. More preferably, thepromoter sequence (a) is situated ahead of the nucleic acid sequence (b)on the nucleic acid molecule (in the 5′→3′ orientation). It is likewisepreferred that, between the two nucleic acid sequences (a) and (b),there are no nucleic acid sequences which reduce the transcription rateof the nucleic acid sequence (b) encoding the protein. All the abovestatements refer to that DNA strand which contains the nucleic acidsequence (b) encoding the protein (the coding strand) and not to theassociated complementary DNA strand. Starting from the nucleic acidsequence (b) encoding the protein, the promoter sequence (a) isconsequently preferably situated further upstream, i.e., in the 5′direction, on this DNA strand.

The nucleic acid sequence b) encodes the protein to be secreted. In thiscase, it is that protein which is to be prepared using an expressionvector according to the invention (target protein).

The protein encoded by the nucleic acid sequence b) comprises a signalpeptide having an amino acid sequence which is at least 80% identical tothe amino acid sequence specified in SEQ ID NO: 2 or is at least 80%identical to the amino acid sequence specified in SEQ ID NO: 4 or is atleast 80% identical to the amino acid sequence specified in SEQ ID NO:6. It was found that such signal peptides bring about efficientsecretion of the protein comprising them, more particularly recombinantprotein. With increasing preference, the signal peptide comprises anamino acid sequence which is at least 81%, 82%, 83%, 84%, 85%, 86%, 87%,88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% and veryparticularly preferably 100% identical to the amino acid sequencespecified in SEQ ID NO: 2, or is at least 81%, 82%, 83%, 84%, 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% and veryparticularly preferably 100% identical to the amino acid sequencespecified in SEQ ID NO: 4, or is at least 81%, 82%, 83%, 84%, 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% and veryparticularly preferably 100% identical to the amino acid sequencespecified in SEQ ID NO: 6. With particular preference, the signalpeptide has an amino acid sequence which is at least 80%, 81%, 82%, 83%,84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%,98%, 99% and very particularly preferably 100% identical to the aminoacid sequence specified in SEQ ID NO: 2, or is at least 80%, 81%, 82%,83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%,97%, 98%, 99% and very particularly preferably 100% identical to theamino acid sequence specified in SEQ ID NO: 4, or is at least 80%, 81%,82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99% and very particularly preferably 100% identical tothe amino acid sequence specified in SEQ ID NO: 6.

Very particular preference is given to the 100% identical sequences ineach case, and so a correspondingly preferred expression vector ischaracterized in that the signal peptide encoded by the nucleic acidsequence b) has an amino acid sequence according to SEQ ID NO: 2, SEQ IDNO: 4 or SEQ ID NO: 6. Particularly preferred nucleic acid sequencesencoding such signal peptides are specified in SEQ ID NO: 1, SEQ ID NO:3 and SEQ ID NO: 5.

Instead of the aforementioned signal peptides which allow secretion ofthe protein, it is further possible to use sequences which arestructurally homologous to these sequences. A structurally homologoussequence is understood to mean an amino acid sequence which has asuccession of amino acids which exhibits spatial folding comparable tothat of a signal peptide having the amino acid sequence according to SEQID NO: 2, SEQ ID NO: 4 or SEQ ID NO: 6. This spatial folding enables itto be recognized by the host cell as a secretory signal sequence and,consequently, the protein comprising the structurally homologous signalsequence to be transferred out of the host cell. Preferably, aninteraction takes place with the translocation system used by the hostcell. Therefore, the structurally homologous amino acid sequence bindspreferably directly or indirectly to at least one component of thetranslocation system of the host cell. Direct binding is understood tomean a direct interaction, and indirect binding is understood to meanthat the interaction can take place via one or more further components,more particularly proteins or other molecules, which act as adaptersand, accordingly, function as a bridge between the structurallyhomologous amino acid sequence and a component of the translocationsystem of the host cell.

The identity of nucleic acid or amino acid sequences is determined by asequence comparison. Such a comparison is achieved by assigning similarsuccessions in the nucleotide sequences or amino acid sequences to oneanother. Said sequence comparison is preferably carried out on the basisof the BLAST algorithm, which is established in the prior art andcommonly used (cf. for example Altschul, S. F., Gish, W., Miller, W.,Myers, E. W. & Lipman, D. J. (1990) “Basic local alignment search tool.”J. Mol. Biol. 215: 403-410, and Altschul, Stephan F., Thomas L. Madden,Alejandro A. Schaffer, Jinghui Zhang, Hheng Zhang, Webb Miller, andDavid J. Lipman (1997): “Gapped BLAST and PSI-BLAST: a new generation ofprotein database search programs”; Nucleic Acids Res., 25, pages3389-3402), and occurs principally by assigning similar successions ofnucleotides or amino acids in the nucleic acid or amino acid sequencesto one another. A tabular assignment of the positions in question isreferred to as an alignment. A further algorithm available in the priorart is the FASTA algorithm. Sequence comparisons (alignments), moreparticularly multiple sequence comparisons, are usually created usingcomputer programs. Frequently used are, for example, the Clustal series(cf. for example Chenna et al. (2003): Multiple sequence alignment withthe Clustal series of programs. Nucleic Acid Research 31, 3497-3500),T-Coffee (cf. for example Notredame et al. (2000): T-Coffee: A novelmethod for multiple sequence alignments. J. Mol. Biol. 302, 205-217) orprograms which are based on these programs or algorithms. For thepurposes of the present invention, sequence comparisons and alignmentsare preferably created using the computer program Vector NTI® Suite 10.3(Invitrogen Corporation, 1600 Faraday Avenue, Carlsbad, Calif., USA)using the predefined standard (default) parameters.

Such a comparison makes it possible to reveal the similarity of thecompared sequences to one another. It is usually reported in percentidentity, i.e., the proportion of identical nucleotides or amino acidresidues on the same positions or positions corresponding to one anotherin an alignment. The broadened term of homology takes conserved aminoacid substitutions into consideration in the case of amino acidsequences, i.e., amino acids having similar properties, because theyusually exercise similar activities or functions within the protein.Therefore, the similarity of the compared sequences can also be reportedas percent homology or percent similarity. Identity and/or homologyvalues can be reported across entire polypeptides or genes or onlyacross particular regions. Homologous or identical regions of differentnucleic acid or amino acid sequences are therefore defined bycongruities in the sequences. They often have the same or similarfunctions. They can be small and comprise only a few nucleotides oramino acids. Such small regions often exercise essential functions forthe entire activity of the protein. It may therefore be advisable tobase sequence congruities only on particular, possibly small regions.Unless otherwise indicated, identity or homology values in the presentapplication refer, however, to the entire length of the variousindicated nucleic acid or amino acid sequences.

The protein encoded by the nucleic acid sequence b) further comprises afurther amino acid sequence. Said amino acid sequence is consequentlythe actual amino acid sequence of the protein without signal peptide.Preferably, the amino acid sequence is a mature protein. A matureprotein is understood to mean the form thereof processed to completion,since it is possible that an associated gene encodes an immature formwhich, after translation, is additionally processed to give the matureform. For example, immature forms of the protein can comprise signalpeptides and/or propeptides or elongations at the N-terminus and/orC-terminus which are no longer present in the mature form. For example,immature forms of proteases, more particularly subtilases and amongthese especially subtilisins, comprise a signal peptide and also apropeptide, which are no longer present in the mature form of theprotease. Alternatively, the further amino acid sequence is the aminoacid sequence of an immature protein which comprises a propeptide. Suchan embodiment comes into consideration especially also for proteases,more particularly subtilases and among these especially subtilisins. Inparticularly preferred embodiments, the further amino acid sequence doesnot comprise a further signal peptide. In such embodiments according tothe invention, only the signal peptide according to the inventionconsequently brings about the secretion of the protein from a host cell.

Particularly preferably, the further amino acid sequence of the proteincomprises the amino acid sequence of an enzyme, more particularly aprotease, amylase, cellulase, hemicellulase, mannanase, tannase,xylanase, xanthanase, xyloglucanase, β-glucosidase, a pectin-cleavingenzyme, carrageenase, perhydrolase, oxidase, oxidoreductase or a lipase,more particularly an enzyme as indicated below. Very particularlypreferably, the further amino acid sequence of the protein comprises theamino acid sequence of a protease and this includes a subtilisin.

For example, one of the enzymes mentioned below can be advantageouslyprepared using an expression vector according to the invention.

Among the proteases, subtilisins are preferred. Examples thereof are thesubtilisins BPN′ and Carlsberg, the protease PB92, the subtilisins 147and 309, the alkaline protease from Bacillus lentus, subtilisin DY andthe enzymes which should be assigned to the subtilases, but no longer tothe subtilisins in the narrower sense, these being thermitase,proteinase K and the proteases TW3 and TW7. Subtilisin Carlsberg isavailable in a further developed form under the trade name Alcalase®from Novozymes A/S, Bagsværd, Denmark. The subtilisins 147 and 309 aresold by Novozymes under the trade names Esperase®, or Savinase®. Derivedfrom the DSM 5483 protease from Bacillus lentus are the proteasevariants known by the name BLAP®. Further preferred proteases are,furthermore, the enzymes known by the name PUR for example. Furtherproteases are, furthermore, the enzymes available under the trade namesDurazym®, Relase®, Everlase®, Nafizym®, Natalase®, Kannase® and Ovozyme®from Novozymes, the enzymes available under the trade names Purafect®,Purafect® OxP, Purafect® Prime, Excellase® and Properase® from Genencor,the enzyme available under the trade name Protosol® from AdvancedBiochemicals Ltd., Thane, India, the enzyme available under the tradename Wuxi® from Wuxi Snyder Bioproducts Ltd., China, the enzymesavailable under the trade names Proleather® and Protease P® from AmanoPharmaceuticals Ltd., Nagoya, Japan, and the enzyme available under thename Proteinase K-16 from Kao Corp., Tokyo, Japan. Also preferred are,furthermore, the proteases from Bacillus gibsonii and Bacillus pumilus,which are disclosed in the international patent applicationsWO2008/086916 and WO2007/131656.

Examples of amylases are the α-amylases from Bacillus licheniformis,from Bacillus amyloliquefaciens or from Bacillus stearothermophilus and,in particular, also the further developments thereof improved for use inwashing agents or cleaning agents. The enzyme from Bacilluslicheniformis is available from Novozymes under the name Termamyl® andfrom Danisco/Genencor under the name Purastar®ST. Products from furtherdevelopment of this α-amylase are available from Novozymes under thetrade names Duramyl® and Termamyl® ultra, from Danisco/Genencor underthe name Purastar® OxAm, and from Daiwa Seiko Inc., Tokyo, Japan, asKeistase®. The α-amylase of Bacillus amyloliquefaciens is sold byNovozymes under the name BAN®, and derived variants of the α-amylasefrom Bacillus stearothermophilus are likewise sold by Novozymes underthe names BSG® and Novamyl®. Furthermore, the α-amylase from Bacillussp. A 7-7 (DSM 12368) and the cyclodextrin glucanotransferase (CGTase)from Bacillus agaradherens (DSM 9948) should be mentioned. Similarly,fusion products of all the aforementioned molecules are usable.Moreover, the further developments of the α-amylase from Aspergillusniger and A. oryzae are suitable, said further developments beingavailable under the trade names Fungamyl® from Novozymes. Furtheradvantageous commercial products are, for example, the amylase Powerase®from Danisco/Genencor and the amylases Amylase-LT®, Stainzyme® andStainzyme Plus®, the latter from Novozymes. Variants of these enzymesobtainable by point mutations can also be prepared according to theinvention. Further preferred amylases are disclosed in the internationalpublished specifications WO 00/60060, WO 03/002711, WO 03/054177 and WO07/079938, the disclosure of which is therefore expressly incorporatedherein by reference and the relevant disclosure content of which istherefore expressly incorporated into the present patent application.Amylases to be prepared according to the invention are, furthermore,preferably α-amylases.

Examples of lipases or cutinases are the lipases originally available,or further developed, from Humicola lanuginosa (Thermomyceslanuginosus), more particularly those with the amino acid substitutionD96L. They are sold, for example, by Novozymes under the trade namesLipolase®, Lipolase® Ultra, LipoPrime®, Lipozyme® and Lipex®. Inaddition, it is possible to prepare, for example, the cutinases whichhave been originally isolated from Fusarium solani pisi and Humicolainsolens. From Danisco/Genencor, it is possible to prepare, for example,the lipases or cutinases whose starting enzymes have been originallyisolated from Pseudomonas mendocina and Fusarium solanii. Furtherimportant commercial products which should be mentioned are thepreparations M1 Lipase® and Lipomax® originally sold by Gist-Brocades(now Danisco/Genencor) and the enzymes sold by Meito Sangyo KK, Japan,under the names Lipase MY-30®, Lipase OF® and Lipase PL®, andfurthermore the product Lumafast® from Danisco/Genencor.

Examples of cellulases (endoglucanases, EG) comprise sequences of thefungal, endoglucanase(EG)-rich cellulase preparation, or the furtherdevelopments thereof, which is supplied by Novozymes under the tradename Celluzyme®. The products Endolase® and Carezyme®, likewiseavailable from Novozymes, are based on the 50 kD EG and the 43 kD EG,respectively, from Humicola insolens DSM 1800. Further commercialproducts of said company which can be prepared are Cellusoft®, Renozyme®and Celluclean®. It is additionally possible to prepare, for example,cellulases which are available from AB Enzymes, Finland, under the tradenames Ecostone® and Biotouch® and which are at least partly based on the20 kD EG from Melanocarpus. Further cellulases from AB Enzymes areEconase® and Ecopulp®. Further suitable cellulases are from Bacillus sp.CBS 670.93 and CBS 669.93, the one from Bacillus sp. CBS 670.93 beingavailable from Danisco/Genencor under the trade name Puradax®. Furthercommercial products of Danisco/Genencor which can be prepared are“Genencor detergent cellulase L” and IndiAge® Neutra.

Variants of these enzymes obtainable by point mutations can also beprepared according to the invention. Particularly preferred cellulasesare Thielavia terrestris cellulase variants which are disclosed in theinternational published specification WO 98/12307, cellulases fromMelanocarpus, more particularly Melanocarpus albomyces, which aredisclosed in the international published specification WO 97/14804,EGIII cellulases from Trichoderma reesei which are disclosed in theEuropean patent application EP 1 305 432 or variants obtainabletherefrom, more particularly those which are disclosed in the Europeanpatent applications EP 1240525 and EP 1305432, and also cellulases whichare disclosed in the international published specifications WO1992006165, WO 96/29397 and WO 02/099091. The respective disclosuresthereof are therefore expressly incorporated herein by reference and therelevant disclosure content thereof is therefore expressly incorporatedinto the present patent application.

Furthermore, it is possible to prepare further enzymes which are coveredby the term hemicellulases. These include, for example, mannanases,xanthan lyases, xanthanases, xyloglucanases, xylanases, pullulanases,pectin-cleaving enzymes and β-glucanases. The β-glucanase obtained fromBacillus subtilis is available under the name Cereflo® from Novozymes.Hemicellulases particularly preferred according to the invention aremannanases, which are sold, for example, under the trade names Mannaway®from Novozymes or Purabrite® from Genencor. For the purposes of thepresent invention, the pectin-cleaving enzymes likewise include enzymeshaving the names pectinase, pectate lyase, pectinesterase, pectindemethoxylase, pectin methoxylase, pectin methylesterase, pectase,pectin methylesterase, pectinoesterase, pectin pectylhydrolase, pectindepolymerase, endopolygalacturonase, pectolase, pectin hydrolase, pectinpolygalacturonase, endopolygalacturonase, poly-α-1,4-galacturonideglycanohydrolase, endogalacturonase, endo-D-galacturonase, galacturan1,4-α-galacturonidase, exopolygalacturonase, polygalacturonatehydrolase, exo-D-galacturonase, exo-D-galacturonanase,exopoly-D-galacturonase, exo-poly-α-galacturonosidase,exopolygalacturonosidase or exopolygalacturanosidase. Examples ofenzymes suitable in this regard are, for example, available under thenames Gamanase®, Pektinex AR®, X-Pect® or Pectaway® from Novozymes,under the name Rohapect UF®, Rohapect Rohapect PTE100®, Rohapect MPE®,Rohapect MA plus HC, Rohapect DA12L®, Rohapect 10L®, Rohapect B1L® fromAB Enzymes, and under the name Pyrolase® from Diversa Corp., San Diego,Calif., USA.

Furthermore, it is also possible to prepare oxidoreductases, for exampleoxidases, oxygenases, catalases, peroxidases, such as haloperoxidases,chloroperoxidases, bromoperoxidases, lignin peroxidases, glucoseperoxidases or manganese peroxidases, dioxygenases or laccases (phenoloxidases, polyphenol oxidases). Suitable commercial products whichshould be mentioned are Denilite® 1 and 2 from Novozymes. Furtherenzymes are disclosed in the international patent applications WO98/45398, WO 2005/056782, WO 2004/058961 and WO 2005/124012.

In a further embodiment of the invention, the further amino acidsequence is not naturally present together with the signal peptide in apolypeptide chain in a microorganism. Consequently, the protein encodedby the nucleic acid sequence b) is a recombinant protein. Not naturallypresent means, therefore, that the two amino acid sequences are notconstituents of an endogenous protein of the microorganism. A proteincomprising the signal peptide and the further amino acid sequenceconsequently cannot be expressed in the microorganism by a nucleic acidsequence which is part of the chromosomal DNA of the microorganism inits wild-type form. Such a protein and/or the nucleic acid sequenceencoding it in each case is consequently not present in the wild-typeform of the microorganism and/or cannot be isolated from the wild-typeform of the microorganism. Both sequences—signal peptide and furtheramino acid sequence—must therefore be assigned to two differentpolypeptide chains in a wild-type form of a microorganism, if both are,or may be, present at all in the wild-type form of a microorganism. Inthe context of this embodiment of the invention, signal peptide andfurther amino acid sequence, or the nucleic acids encoding them, weretherefore newly combined using gene-technology methods, and thiscombination of signal peptide and further amino acid sequence does notexist in nature. In the wild-type form of a microorganism, such alinkage of the signal peptide with the further amino acid sequence isconsequently not present, specifically neither on the DNA level nor onthe protein level. However, the signal peptide and the further aminoacid sequence, or the nucleic acid sequences encoding them both, canboth be of natural origin, but the combination thereof does not exist innature. Signal peptide and further amino acid sequence themselves can,however, originate from the same microorganism or else from differentmicroorganisms.

In a preferred embodiment, a nucleic acid according to the invention ischaracterized in that it is a nonnatural nucleic acid. Nonnatural meansthat a nucleic acid according to the invention cannot be isolated froman organism in its wild-type form that occurs in nature. Moreparticularly and with regard to wild-type bacteria, a nucleic acidaccording to the invention is therefore not a nucleic acid endogenous tobacteria.

Preferably, the sequences (a) and (b) do not originate from the sameorganism(s), more particularly bacteria, but instead originate fromdifferent organisms, more particularly bacteria. Different bacteria are,for example, bacteria which belong to different strains or species orgenera.

In a further embodiment of the invention, the expression vector ischaracterized in that the signal peptide is arranged N-terminal to thefurther amino acid sequence in the protein encoded by the nucleic acidsequence b). The protein encoded by the nucleic acid sequence b)therefore has the following structure: N-terminus—signalpeptide—(optional additional amino acid sequence)—further amino acidsequence—C-terminus. Such a structure of the protein to be expressed hasbeen found to be particularly advantageous.

In a further embodiment of the invention, the expression vector ischaracterized in that the protein encoded by the nucleic acid sequenceb) further comprises a connecting sequence arranged between the signalpeptide and the further amino acid sequence of the protein. The proteinencoded by the nucleic acid sequence b) therefore has the followingstructure: N-terminus—signal peptide—connecting sequence (also “coupler”or “spacer”)—further amino acid sequence—C-terminus. Such a structure ofthe protein to be expressed has likewise been found to be particularlyadvantageous. Preferably, the length of the connecting sequence isbetween 1 and 50 amino acids, between 2 and 25 amino acids, between 2and 15 amino acids, between 3 and 10 amino acids, and particularlypreferably between 3 and 5 amino acids. An example of a particularlypreferred connecting sequence is the succession of amino acids ofalanine, glutamic acid and phenylalanine (from the N-terminus to theC-terminus).

In a further embodiment of the invention, the expression vector ischaracterized in that the further amino acid sequence of the proteincomprises the amino acid sequence of a protease, said amino acidsequence of the protease being at least 80% identical to SEQ ID NO: 7.Preferably, the amino acid sequence of the protease is at least 81%,82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99% and very particularly preferably 100% identical toSEQ ID NO: 7.

Alternatively, the further amino acid sequence of the protein comprisesthe amino acid sequence of a protease which is at least 80% identical toSEQ ID NO: 8. Preferably, the amino acid sequence of the protease is atleast 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, 99% and very particularly preferably 100%identical to SEQ ID NO: 8.

Alternatively, the further amino acid sequence of the protein comprisesthe amino acid sequence of a protease which is at least 80% identical toSEQ ID NO: 9. Preferably, the amino acid sequence of the protease is atleast 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, 99% and very particularly preferably 100%identical to SEQ ID NO: 9.

Alternatively, the further amino acid sequence of the protein comprisesthe amino acid sequence of a protease which is at least 80% identical toSEQ ID NO: 10 and has the amino acid glutamic acid (E) or aspartic acid(D) at position 99 in the numbering according to SEQ ID NO: 10.Preferably, the amino acid sequence of the protease is at least 81%,82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99% identical and very particularly preferably identicalto SEQ ID NO: 10 in positions 1 to 98 and 100 to 269 in the numberingaccording to SEQ ID NO: 10.

Alternatively, the further amino acid sequence of the protein comprisesthe amino acid sequence of a protease which is at least 80% identical toSEQ ID NO: 10 and has the amino acid glutamic acid (E) or aspartic acid(D) at position 99 in the numbering according to SEQ ID NO: 10 and has,furthermore, at least one of the following amino acids in the numberingaccording to SEQ ID NO: 10:

(a) threonine at position 3 (3T),

(b) isoleucine at position 4 (4I),

(c) alanine, threonine or arginine at position 61 (61A, 61T or 61R),

(d) aspartic acid or glutamic acid at position 154 (154D or 154E),

(e) proline at position 188 (188P),

(f) methionine at position 193 (193M),

(g) isoleucine at position 199 (199I),

(h) aspartic acid, glutamic acid or glycine at position 211 (211 D, 211Eor 211G),

(i) combinations of the amino acids (a) to (h).

Preferably, the amino acid sequence of this protease is at least 81%,82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99% identical and very particularly preferably identicalto SEQ ID NO: 10 in all positions which are not modified or not intendedfor modification. Very particularly preferably, the further amino acidsequence of the protein therefore comprises the amino acid sequence of aprotease which has an amino acid sequence modified in at least twopositions with respect to SEQ ID NO: 10, with the first modificationbeing glutamic acid at position 99 in the numbering according to SEQ IDNO: 10 and the second modification, in the numbering according to SEQ IDNO: 10, being selected from the group consisting of:

(a) threonine at position 3 (3T),

(b) isoleucine at position 4 (4I),

(c) alanine, threonine or arginine at position 61 (61A, 61T or 61R),

(d) aspartic acid or glutamic acid at position 154 (154D or 154E),

(e) proline at position 188 (188P),

(f) methionine at position 193 (193M),

(g) isoleucine at position 199 (199I),

(h) aspartic acid, glutamic acid or glycine at position 211 (211 D, 211Eor 211G),

(i) combinations of the amino acids (a) to (h).

Likewise very particularly preferably, the further amino acid sequenceof the protein comprises the amino acid sequence of a protease which hasan amino acid sequence modified in at least two positions with respectto SEQ ID NO: 10, with the first modification being aspartic acid atposition 99 in the numbering according to SEQ ID NO: 10 and the secondmodification, in the numbering according to SEQ ID NO: 10, beingselected from the group consisting of:

(a) threonine at position 3 (3T),

(b) isoleucine at position 4 (4I),

(c) alanine, threonine or arginine at position 61 (61A, 61T or 61R),

(d) aspartic acid or glutamic acid at position 154 (154D or 154E),

(e) proline at position 188 (188P),

(f) methionine at position 193 (193M),

(g) isoleucine at position 199 (199I),

(h) aspartic acid, glutamic acid or glycine at position 211 (211 D, 211Eor 211G),

(i) combinations of the amino acids (a) to (h).

It was found that the abovementioned proteases can also be preparedparticularly advantageously using expression vectors according to theinvention. For such embodiments of the invention, it was found that suchcombinations of signal peptides and subtilisins make it possible toachieve particularly good product yields in a fermentation procedure.Specified in this regard are the amino acid sequences of the matureproteases, i.e., the products processed to completion. In an expressionvector according to the invention, it is also possible in this regard toinclude further sequences of the immature protease, more particularlypropeptides for example. In such a case, the further amino acid sequenceof the protein comprises the amino acid sequence of the protease and ofthe propeptide. A further embodiment of the invention is consequentlycharacterized in that the further amino acid sequence of the proteincomprises the amino acid sequence of a protease, more particularly aprotease as described above, together with a propeptide or itspropeptide.

In general, the further amino acid sequence of the protein need notmerely comprise the amino acid sequence of a mature protein; on thecontrary, it is possible to include further amino acid sequences suchas, for example, propeptides of said amino acid sequence. This appliesnot only to proteases, but also to all proteins, more particularly allother types of enzymes.

Nucleic acids and expression vectors according to the invention can begenerated via methods known per se for modifying nucleic acids. Suchmethods are, for example, presented in relevant manuals such as the oneby Fritsch, Sambrook and Maniatis, “Molecular cloning: a laboratorymanual”, Cold Spring Harbor Laboratory Press, New York, 1989, andfamiliar to a person skilled in the art in the field of biotechnology.Examples of such methods are chemical synthesis or the polymerase chainreaction (PCR), optionally in conjunction with further standard methodsin molecular biology and/or chemistry or biochemistry.

Nonhuman host cells containing vectors according to the invention,preparations methods in which corresponding host cells are used, and theuses of corresponding vectors or host cells are associated with allaforementioned inventive subject matter and embodiments as furtherinventive subject matter. Therefore, the above statements relatecorrespondingly to said inventive subject matter.

The invention further provides a nonhuman host cell containing anexpression vector according to the invention. An expression vectoraccording to the invention is preferably introduced into the host cellby the transformation thereof. According to the invention, this ispreferably carried out by transforming a vector according to theinvention into a microorganism, which then constitutes a host cellaccording to the invention. Alternatively, it is also possible forindividual components, i.e., nucleic acid portions or fragments, forexample the components (a) and/or (b), of a vector according to theinvention to be introduced into a host cell in such a way that the thusresulting host cell comprises a vector according to the invention. Thisapproach is especially suitable if the host cell already comprises oneor more constituents of a vector according to the invention and thefurther constituents are then complemented accordingly. Methods fortransforming cells are established in the prior art and well known to aperson skilled in the art. In principle, all cells, i.e., prokaryotic oreukaryotic cells, are suitable as host cells. Host cells which can beadvantageously manipulated genetically, for example with regard totransformation with the vector and the stable establishment thereof, arepreferred, for example unicellular fungi or bacteria. In addition,preferred host cells are easily manipulatable from a microbiological andbiotechnological perspective. This concerns, for example, ease ofculture, high growth rates, low demands on fermentation media, and goodproduction and secretion rates for foreign proteins. In many cases, itis necessary to determine experimentally the optimal expression systemsfor each individual case from the abundance of different systemsavailable in the prior art.

Further preferred embodiments are host cells which are regulatable interms of their activity owing to genetic regulatory elements which, forexample, are made available on the vector, but may also be present insaid cells from the start. For example, they can be stimulated toexpress by controlled addition of chemical compounds serving asactivators, by changing the culture conditions, or upon attainment of aparticular cell density. This allows economical production of theproteins.

Preferred host cells are prokaryotic or bacterial cells. Bacteria haveshort generation times and low demands in terms of culture conditions.As a result, it is possible to establish cost-effective methods. Inaddition, a wealth of experience is available to a person skilled in theart in the case of bacteria in fermentation technology. For a specificproduction process, Gram-negative or Gram-positive bacteria may besuitable for a very wide variety of different reasons which are to bedetermined experimentally on an individual basis, such as nutrientsources, rate of product formation, time requirement, etc.

In the case of Gram-negative bacteria, for example Escherichia coli, amultiplicity of polypeptides are secreted into the periplasmic space,i.e., into the compartment between the two membranes encasing the cells.This may be advantageous for specific applications. Furthermore, it isalso possible to configure Gram-negative bacteria in such a way thatthey eject the expressed polypeptides not only into the periplasmicspace, but also into the medium surrounding the bacterium. By contrast,Gram-positive bacteria, for example Bacilli or Actinomycetaceae or otherrepresentatives of the Actinomycetales, do not have an outer membrane,and so secreted proteins are immediately released into the mediumsurrounding the bacteria, generally the culture medium, from which theexpressed polypeptides can be purified. They can be isolated directlyfrom the medium or processed further. In addition, Gram-positivebacteria are related or identical to most organisms of origin fortechnically important enzymes and usually themselves form comparableenzymes, and so they have similar codon usage and theirprotein-synthesis apparatus is naturally organized accordingly.

Codon usage is understood to mean the rendering of the genetic code intoamino acids, i.e., which nucleotide order (triplet or base triplet)encodes which amino acid or which function, for example the start andend of the region to be translated, binding sites for various proteins,etc. Thus, each organism, more particularly each production strain, hasa particular codon usage. Bottlenecks can occur in protein biosynthesisif the codons on the transgenic nucleic acid in the host cell are facedwith a comparatively low number of loaded tRNAs. By contrast, synonymouscodons encode the same amino acids and can be translated moreefficiently depending on the host. This optionally necessarytranscription thus depends on the choice of expression system.Especially in the case of samples composed of unknown, possiblyunculturable organisms, a corresponding adaptation may be necessary.

The present invention is, in principle, applicable to allmicroorganisms, more particularly all fermentable microorganisms,particularly preferably those of the genus Bacillus, and results in itbeing possible to realize, through the use of such microorganisms asproduction organisms, an increased product yield in a fermentationprocedure. Such microorganisms are preferred host cells for the purposesof the invention.

In a further embodiment of the invention, the host cell is thereforecharacterized in that it is a bacterium, preferably one selected fromthe group of the genera of Escherichia, Klebsiella, Bacillus,Staphylococcus, Corynebacterium, Arthrobacter, Streptomyces,Stenotrophomonas and Pseudomonas, more preferably one selected from thegroup of Escherichia coli, Klebsiella planticola, Bacilluslicheniformis, Bacillus lentus, Bacillus amyloliquefaciens, Bacillussubtilis, Bacillus alcalophilus, Bacillus globigii, Bacillus gibsonii,Bacillus clausii, Bacillus halodurans, Bacillus pumilus, Staphylococcuscarnosus, Corynebacterium glutamicum, Arthrobacter oxidans, Streptomyceslividans, Streptomyces coelicolor and Stenotrophomonas maltophilia. Veryparticular preference is given to Bacillus licheniformis.

However, the host cell may also be a eukaryotic cell, characterized inthat it has a nucleus. The invention therefore further provides a hostcell, characterized in that it has a nucleus.

In contrast to prokaryotic cells, eukaryotic cells are capable ofposttranslationally modifying the protein formed. Examples thereof arefungi such as Actinomycetaceae or yeasts such as Saccharomyces orKluyveromyces. This may be particularly advantageous when, for example,the proteins are to undergo, in conjunction with their synthesis,specific modifications, which is allowed by such systems. Modificationswhich eukaryotic systems carry out especially in conjunction withprotein synthesis include, for example, the binding oflow-molecular-weight compounds such as membrane anchors oroligosaccharides. Such oligosaccharide modifications may, for example,be desirable for lowering the allergenicity of an expressed protein.Coexpression with the enzymes naturally formed by such cells, forexample cellulases, may also be advantageous. Furthermore, thermophilicfungal expression systems may, for example, be especially suitable forthe expression of temperature-resistant variants.

For the purposes of the invention, proteins encoded by the nucleic acidsequence (b), more particularly those as described above, are consideredto be the products formed during fermentation. They are thereforepreferably enzymes, particularly preferably proteases, and veryparticularly preferably subtilisins.

Furthermore, the host cells can be modified with respect to theirrequirements in terms of culture conditions, can have other oradditional selection markers, or can express other or additionalproteins. More particularly, the host cells can be those which expressmultiple proteins or enzymes. Preferably, they secrete them into themedium surrounding the host cells.

The host cells according to the invention are cultured and fermented ina manner known per se, for example in batch systems or continuoussystems. In the first case, an appropriate culture medium is inoculatedwith the host cells and the product harvested from the medium after aperiod to be determined experimentally. Continuous fermentationprocedures involve attaining a steady state in which, over acomparatively long period, cells partly die but also grow again andproduct can be removed at the same time from the medium.

Host cells according to the invention are preferably used to prepareproteins encoded by the nucleic acid sequence (b). The inventiontherefore further provides a method for preparing a protein, comprising

a) culturing a host cell according to the invention

b) isolating the protein from the culture medium or from the host cell.

This inventive subject matter preferably comprises fermentation methods.Fermentation methods are known per se from the prior art and constitutethe actual industrial-scale production step, generally followed by anappropriate purification method for the product prepared, for examplethe protein. All fermentation methods involving a corresponding methodfor preparing a protein constitute embodiments of this inventive subjectmatter.

In this connection, the various optimal conditions for the preparationmethods, more particularly the optimal culture conditions for the hostcells used, must be determined experimentally according to the knowledgeof a person skilled in the art, for example with respect to fermentationvolume and/or media composition and/or oxygen supply and/or stirrerspeed.

Fermentation methods characterized in that the fermentation is carriedout via a continuous supply strategy are one particular possibility. Inthis case, the media constituents which are consumed by the ongoingculture are continuously fed; this is also known as a continuous feedstrategy. As a result, considerable increases both in the cell densityand in the cell mass or dry mass and/or especially the activity of theprotein of interest, preferably an enzyme, can be attained.

Furthermore, the fermentation can also be configured in such a way thatunwanted metabolic products are filtered out or neutralized by additionof buffer or of counterions appropriate in each case.

The prepared protein can be harvested from the fermentation medium. Sucha fermentation method is advantageous over isolation of the polypeptidefrom the host cell, i.e., product processing from the cell mass (drymass). According to the invention, secretion markers suitable in thisregard are provided with the signal peptides.

All facts explained above can be combined to form methods for preparingproteins. In this regard, a multiplicity of possible combinations ofmethod steps is conceivable. The optimal method must be determined foreach specific individual case.

The invention further provides for the use of an expression vectoraccording to the invention or of a host cell according to the inventionfor preparing a protein.

All facts, subject matter and embodiments which are already describedabove are also applicable to this inventive subject matter. Therefore,reference is expressly made at this point to the disclosure at thecorresponding point with the indication that said disclosure alsoapplies to the uses according to the invention (use of the vector or ofthe host cell).

EXAMPLES

All molecular biology work steps follow standard methods, as specified,for example, in the manual from Fritsch, Sambrook and Maniatis“Molecular cloning: a laboratory manual”, Cold Spring Harbor LaboratoryPress, New York, 1989, or comparable relevant works. Enzymes and kitswere used according to the instructions from the respectivemanufacturers.

Example 1: Preparation of Expression Vectors According to the Invention

The plasmid pBSMuL3 (Brockmeier et al., 2006) was shortened by SacIrestriction digestion and subsequent relegation around the E. coliportion. The resulting plasmid, pBSMuL5 (cf. FIG. 1), was used as avector for cloning the proteases including propeptide into the EcoRI andBamHI restriction sites. To this end, amplification was carried out ofthe genes of the protease according to SEQ ID NO: 8 with the primersaccording to SEQ ID NO: 11 and SEQ ID NO: 12, and of the alkalineprotease according to SEQ ID NO: 9 with the primers according to SEQ IDNO: 13 and SEQ ID NO: 14. The resulting plasmids were used as vectorsfor cloning the signal peptides into the HindIII and EcoRI restrictionsites. The DNA fragment of the control signal peptide SubC (B.licheniformis, NCBI (National Center for Biotechnology Information)accession number: X91260.1), as benchmark, was amplified using theprimers according to SEQ ID NO: 15 and SEQ ID NO: 16 and cloned in eachcase into the HindIII and EcoRI restriction sites of the plasmids,producing plasmids having a nucleic acid sequence b) encoding a proteinhaving the signal peptide SubC in conjunction with a protease accordingto SEQ ID NO: 8 (plasmid 1) or SEQ ID NO: 9 (plasmid 2). These plasmidswere subsequently used as control or benchmark. The DNA fragment of thesignal peptide according to SEQ ID NO: 2 was amplified using the primersaccording to SEQ ID NO: 19 and SEQ ID NO: 20, the DNA fragment of thesignal peptide according to SEQ ID NO: 4 was amplified with the primersaccording to SEQ ID NO: 17 and SEQ ID NO: 18, and the DNA fragment ofthe signal peptide according to SEQ ID NO: 6 was amplified with theprimers according to SEQ ID NO: 21 and SEQ ID NO: 22. Whereas the DNAfragments of the signal peptides according to SEQ ID NO: 2 and 4 wereeach cloned into the vector encoding a protease according to SEQ ID NO:8 (plasmids 3 and 4), the DNA fragment of the signal peptide accordingto SEQ ID NO: 6 was inserted into the vector encoding a proteaseaccording to SEQ ID NO: 9 (plasmid 5). Associated with the cloning, asequence of 9 nucleotides encoding the succession of amino acids AEF(cf. FIG. 1) was introduced between the DNA sequence of the particularsignal peptide and the DNA sequence of the propeptide of the particularprotease. This so-called connecting sequence contains the recognitionsequence of the restriction endonuclease EcoRI.

All oligonucleotides used as primers are listed in table 1 below:

TABLE 1 Nucleotide  sequence (in 5′→3′ orientation; the restrictionRestriction  Name sites are underlined) site SEQ ID NO. 11ATATGAATTCGCTGAGGAA EcoRI GCAAAAGAAAA SEQ ID NO. 12 ATATGGATCCTTAGCGTGTBamHI TGCCGCTTCTGC SEQ ID NO. 13 ATATGAATTCGCTGAGGAA EcoRI GCAAAAGAAAASEQ ID NO. 14 ATATGGATCCTTAGCGCGT BamHI TGCTGCATCTGC SEQ ID NO. 15ATATAAGCTTAAGGAGGAT HindIII ATTATGATGAGGAAAAAGA GTTTT SEQ ID NO. 16ATATGAATTCAGCTGCAGA EcoRI AGCGGAATCGCTGAA SEQ ID NO. 17ATATAAGCTTAAGGAGGAT HindIII ATTATGAAAAAACTATTCA AAACC SEQ ID NO. 18ATATGAATTCAGCAGCCGC EcoRI CGCAGATTGTGAGAA SEQ ID NO. 19ATATAAGCTTAAGGAGGAT HindIII ATTATGGCGAAACCACTAT CAAAA SEQ ID NO. 20ATATGAATTCAGCAGCGTC EcoRI TGCCGCGGGTAAACC SEQ ID NO. 21ATATAAGCTTAAGGAGGAT HindIII ATTATGACATTGACTAAAC TGAAA SEQ ID NO. 22ATATGAATTCAGCGGCAAG EcoRI TGCCTGACTGGAAAA

Example 2: Expression of the Proteins

A Bacillus licheniformis strain was transformed with the plasmids 1 to 5to obtain the various protease production strains. For the inoculationof cultures, use was made of single colonies from agar plates which wereincubated overnight (ON). For the quantitative determination of theefficiency of secretion, the single colonies were transferred directlyfrom the agar plates to deep-well MTPs (microtiter plates; 96 wells eachcontaining 1 mL of selective LB medium). In said determination, eachsingle colony was transferred to at least two wells in parallel in orderto obtain duplicate or triplicate determination as a result of themultiple cultivation of the particular clone. For the inoculation of thedeep-well MTPs, only clones which were incubated overnight at 37° C.were used. After cultivation for 20 h at 37° C. in the microtiter plateshaker (Timix 5 from Edmund-Bühler, Hechingen), all clones werereplicated on LB agar plates and subsequently the cells were sedimentedby centrifugation (4000 rpm, 20 min, 4° C.). All pipetting steps whichfollow were carried out using multichannel pipets (Eppendorf, Hamburg),with the use of the reverse-pipetting mode and no volumes smaller than15 μl being pipetted. In each case, the smallest volume was initiallycharged in the MTP and the larger volumes were added thereto and the MTPwas mixed at each dilution step for 10 seconds in the spectrophotometer“Spectramax 250” (Molecular Devices, Sunnyvale, USA). For the generationof the corresponding dilutions, the culture supernatant was removedusing the multichannel pipet and transferred to microtiter plates (96wells, F-bottom, transparent, from Greiner Bio-One, Frickenhausen).

Subsequently, the proteolytic activity in the culture supernatants ordilutions was determined via the release of the chromophorepara-nitroaniline (pNA) from the substratesuc-L-Ala-L-Ala-L-Pro-L-Phe-p-nitroanilide (suc-AAPF-pNA). The proteasecleaves the substrate and releases pNA. The release of the pNA causes anincrease in the absorbance at 410 nm, its change in time being a measureof the enzymatic activity (cf. Del Mar et al., Anal. Biochem., 99:316-320, 1979).

For the determination of the efficiency of secretion of the variousstrains, an internal control construct (plasmid 1 or plasmid 2) wasconcomitantly cultivated in each MTP cultivation. The proteolyticactivity of the strain having the control construct, as determined inthe culture supernatant, was defined as 100%.

Compared with the control which comprised the plasmid 1, the strainscontaining the plasmids 3 and 4 according to the invention attained aprotease activity which was increased by 194%+/−48 and 230%+/−38,respectively (cf. FIG. 2).

Compared with the control which comprised the plasmid 2, the straincontaining the plasmid 5 according to the invention attained a proteaseactivity which was increased by 44%+/−10 (cf. FIG. 3).

DESCRIPTION OF THE FIGURES

FIG. 1: Diagram of the cloning strategy in the Bacillus expressionvector pBSMul5 (modified from Brockmeier et al., 2006). (A) The DNAfragments of the signal peptides were amplified at the N-terminus with aHindIII restriction site, a standardized ribosome binding site (RBS),followed by a spacer region and the standardized start codon formethionine. A coupler having an alanine at the “+1” position and theEcoRI restriction site was attached between signal peptide andN-terminus of the protease to be secreted. (B) Bacillus vector pBSMul5having the HpaII promoter, the particular secretion target (cloned viaEcoRI and BamHI), and the kanamycin-resistance cassette and thereplication protein repB for Bacillus.

FIG. 2: Relative protease activity in the culture supernatant ofBacillus licheniformis containing the protease according to SEQ ID NO: 8and three different signal peptides in pBSMul5. The proteolytic activityof the construct plasmid 1 was defined as 100% (control). The valueswere determined in at least two independent cultivations. The error barsindicate the standard deviation.

FIG. 3: Relative protease activity in the culture supernatant ofBacillus licheniformis containing the protease according to SEQ ID NO: 9and two different signal peptides in pBSMul5. The proteolytic activityof the construct plasmid 2 was defined as 100% (control). The valueswere determined in at least two independent cultivations. The error barsindicate the standard deviation.

The invention claimed is:
 1. An expression vector comprising: a) apromoter sequence; and b) a nucleic acid sequence which encodes aprotein comprising a signal peptide and a subtilisin, wherein the signalpeptide comprises an amino acid sequence which is at least 95% identicalto the amino acid sequence specified in SEQ ID NO: 2, and wherein theexpression vector achieves improved secretion of the protein from a hostcell containing the expression vector compared to secretion achieved bythe expression vector having a signal peptide other than a signalpeptide of b).
 2. The expression vector of claim 1, wherein the signalpeptide encoded by the nucleic acid sequence b) has the amino acidsequence of SEQ ID NO:
 2. 3. The expression vector of claim 1, whereinthe signal peptide is arranged N-terminal to the subtilisin in theprotein encoded by the nucleic acid sequence b).
 4. The expressionvector of claim 1, wherein the protein encoded by the nucleic acidsequence b) further comprises a connecting sequence arranged between thesignal peptide and the subtilisin of the protein, the length of theconnecting sequence being between 1 and 50 amino acids.
 5. Theexpression vector of claim 1, wherein the subtilisin comprises an aminoacid sequence at least 95% identical to SEQ ID NO:
 8. 6. A nonhuman hostcell comprising the expression vector of claim
 1. 7. The host cell ofclaim 6, wherein it is a bacterium.
 8. A method for preparing a protein,comprising: (a) culturing the host cell of claim 6; and (b) isolatingthe protein from the culture medium or from the host cell.
 9. The hostcell of claim 7, wherein the bacterium is selected from the groupconsisting of the genera of Escherichia, Klebsiella, Bacillus,Staphylococcus, Corynebacterium, Arthrobacter, Streptomyces,Stenotrophomonas and Pseudomonas.
 10. The host cell of claim 7, whereinthe bacterium is selected from the group consisting of the genera ofEscherichia, Klebsiella, Bacillus, Staphylococcus, Corynebacterium,Arthrobacter, Streptomyces, Stenotrophomonas and Pseudomonas.
 11. Thehost cell of claim 7, wherein the bacterium is selected from the groupconsisting of Escherichia coli, Klebsiella planticola, Bacilluslicheniformis, Bacillus lentus, Bacillus amyloliquefaciens, Bacillussubtilis, Bacillus alcalophilus, Bacillus globigii, Bacillus gibsonii,Bacillus clausii, Bacillus halodurans, Bacillus pumilus, Staphylococcuscarnosus, Corynebacterium glutamicum, Arthrobacter oxidans, Streptomyceslividans, Streptomyces coelicolor, and Stenotrophomonas maltophilia. 12.The expression vector of claim 1, wherein improved secretion of theprotein from a host cell containing the expression vector is achievedcompared to secretion achieved by an expression vector having signalpeptide SubC (Bacillus licheniformis).